Low-pressure drop fluid duct bend



March 25, 1952 I\.CZ.55IC:ILJI\P1C) LOW-PRESSURE DROP FLUID DUCT BENDFiled Feb. 3, 1950 Fig.3.

Inventor: Anthoh C. Sicilians,

' L-J His Attorneg.

Patented Mar. 25, 1952 LOW-rPRESSURE DROP FLUID'DUCT BEN D Anthony C}Siciliano; Wesleyville; Pa'., assignor. to General Electric Company,azcorporatiomof.

New York:

Application February 3, 1959; Serial No. 142,185

Claims.

Myinvention relates to bend sections in fluid conveyingducts andmoreparticularly to" the construction of afluid" conveying duct; sectionwhereina change'in the'idirection of fluid flowis accomplishedwith aminimum of loss of pressure of the fluid.

This invention. primarily involves elbows" or bend sections in'rectangular cross-sectidn fluid conveying ducts'suchast'hose'comm'onlyused for conveyingair in' heating and ventilatingsystems or inconveying combustion air. in power plants, butimay be.found useful inducts. for the conveyance ofother. fluids for other.purposes. In sheet metal." duct worlrof' the. type under: conesideration, the. simplest, cheapest and. most obvious bend "constructioncomprises. a. square corner bend with no curvature in the duct surfaceswhatever. It has beenfound that in order to obtain a more eflicient ductbend, that is, one in which a lower: pressure'drop occurs at the benddue to turbulence in the fluid, that the duct bend may be alteredbysub'stitutingradiused surfaces for the square corner bends. However, aradiused bend ismore expensiveand complicated to manufacture than astraight bend and when the innercorner of the bend is radiused, the ductrequires; more space since, in. effect the inn-er corner of .the bendhas been filledin.

It: is, therefore, an object of my invention: to

provide an improved fluid ductihaving essentially the economical squarecorner bend construction but with simple added elements to reduce thepressure drop therein.

My invention, therefore, consists essentially in an improved bendconstruction for fluid conveying ducts of rectangular cross sectionwherein the efficiency of the bend is improved by the addition of curvedsurfaces in the bend, the radii of curvature having a definiterelationship to a dimension of the duct.

For a better and more complete understanding of this invention,reference may be had to the following specification and the accompanyingdrawing wherein Figs. 1 and 2 are perspective views, with cut awaysections, of two embodiments of my invention, and Fig. 3 is a side view,in section, showing an alternative detail of construction which may beused in the embodiments of either Fig. 1 or Fig. 2, and the features ofnovelty are set forth in the appended claims.

Referring now particularly to the drawing, in Fig. 1, there is shown afluid duct bend section I for a rectangular cross-section fluidconveying duct. The duct has a width dimension 2 at the duct surface 3.The ends 4 and 5 of section I 2. are open and. adapted. to be join-ed.withzadditionall duct: sections to form a complete fluid conveying:ductLstructure. The duct bendincludes inner duct surfaces 6 andwhichmeet at:- an: inner; right angle bend or corner 8, andouterduct-asurfaces: 9 and inwhich meet at an outer" right anglebendlorr'corner H. Anadditionalcurved surface; l2; which may comprise aseparate piece of .sheet metaLis added'to the inner; corner: 3'; ofthesbend in. the, interior of the duct... Surface. i2..is.fastened'inplace:at the ends i 3,.and H! :by a; suitable methodfsuchias. welding.

or riveting. Surface lzrisspreferably bentirna. circularcurvesthrough.anangle .ofrlBO. andhaving a diameter; of? curvature. which; is:approximately equal. to. the width dimension 2. The radius of curvaturel 5 is, therefore, approximate- 1y. one-half :of the width dimension )2.More ex-. actly, the ideal.radius-of curvature i 5 is'0.466 times thewidth. dimension 2.

Ithasibeen found that .with this configuration of: duct bend, the lossof pressure, at the bend, of the fluids being conveyedcan be reduced asmuch as;55,%. Anysubstantial increase or. decrease of radius l5 from thevalue stateda'boveresults in 357.1058 of efficiency in terms of anincreased. pressure loss'. However, theradius of curvature l5 can bevaried: over a range from one-quarter of the; width. dimension 2:130thefull Width dimensionz2. withoutdeparting from the spirit of thisinvention;effectingv a. substantial reduction in the loss of. fluidpressure at the bend.

In Fig. 2, there is shown a second embodiment of my invention,designated as a whole as I6. wherein a second curved surface I! isincorporated in the interior of the duct at the outer corner ll of theduct bend, and welded or riveted in place at the ends l8 and IS in aknown manner. Surface I! also has a circular curvature, but of a radius20 equal to one and one-third times the duct width dimension 2. Again asubstantially greater or lesser radius of curvature will reduce theefliciency of the duct bend, but this radius of curvature can also bevaried over a range from one and one-sixth times, to one andthreequarters times the duct width dimension 2 without departing fromthe spirit of this invention, effecting a substantial reduction in theloss of fluid pressure at the bend. With the addition of both curvedsurfaces I2 and I1, the reduction of the pressure drop in the duct bendcan be as much as Since the ideal radius of curvature I5 of surface I2is 0.446 times the width dimension 2 and since the ideal radius ofcurvature 20 of surface I! is equal to one and one-third times the ductwidth dimension 2, the ideal ratio between these radii is 0.466 dividedby one and one-third which equals 0.35.

The transitions, at ends l3 and M, from the curved surface l2 to theflat surfaces 6 and I need not be as abrupt as shown. As illustrated inFig. 3, for instance, surface l2 may include flat surfaces 21, tangentto the curve of surface I2.

It will be seen from the above that I have provided for a duct bendhaving a maximum efficiency while maintaining the economy and simplicityof construction of a square duct bend as well as the space savingproperties thereof. In this connection, it is obvious that inner ductsurfaces 6 and 1 may be concurrently positioned against perpendicularsurfaces which meet to form an angled corner or edge. This edge thenfits into the inner corner 8 of the duct. These surfaces may define theexterior of a structural member, the edge of which cannot be radiused toprovide space for a conventional inner curved duct bend.

It will be understood, of course, that although the above descriptionhas been entirely on the basis of 90 bends, that the invention may alsobe advantageously applied to bends of other angles. Various othermodifications may be made without departing from the invention. Theappended claims are, therefore, intended to cover any such modificationswithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An elbow for a rectangular cross section fluid duct having an angledbend at the inner corner on the exterior surface of said elbow, theinterior surface of said elbow at said corner being curved and having aminimum radius of curvature in the direction of the bend of said elbownot greater than the width of said duct but not less than one quarter ofsaid width, the angle of the arc of said curvature being greater thanthe angle of said elbow.

2. An elbow for a rectangular cross section fluid duct having an angledbend at the inner corner of the exterior of said elbow, the interior ofsaid elbow having curved surfaces at both said inner bend and at theouter corner thereof, said first mentioned curved surface having anelbow and a minlmui'n radius of curvature in the direction of the bendof said elbow not greater than the width of said duct but not less thanone-quarter of said width.

3. 'An elbow for a rectangular cross'section fluid duct, an angled bendat the inner corner of the exterior of said elbow, the interior of saidelbow having curved surfaces at said inner bend and at the outer cornerthereof, said first mentioned curved surface having an angle ofcurvature greater than the angle of said elbow and a radius of curvaturein the direction of the bend of said elbow of the order of one-half thewidth of said duct, said second curved surface having a radius ofcurvature of the order of one and one-third times the width of saidduct.

4. In a rectangular cross section fluid duct, an elbow for joining twoduct sections which are respectively positioned closely against twosurfaces which meet at a right angle, said elbow being fitted aroundsaid right angle but having a minimum radius on the inner surface at theinner corner thereof not greater than the width of said duct but notless than one-quarter of said width, the angle of the arc of saidcurvature being greater than the angle of said elbow.

5. An elbow for a rectangular cross section fluid duct having an angledbend at the inner ANTHONY C. SICILIANO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 562,957 Goff June 30, 18961,984,172 Brownley Dec. 11, 1934 2,147,431 Ewing Feb. 14, 1939 2,216,046Peck Sept. 24, 1940 2,273,818 Childers et al Feb. 24, 1942 2,359,579Peck Oct. 3, 1944

